Ultraviolet (UV) curing has many applications in printing, coating and sterilization. UV-sensitive materials generally rely upon a particular amount of energy in the form of UV light to initiate and sustain the curing process (polymerization) within the materials. UV light fixtures, commonly known as UV lamps, provide the UV light to the materials for curing.
Using arrays of light emitting diodes (LEDs) in UV curing has several advantages over using arc lamps, including lower power consumption, lower cost, cooler operating temperatures, etc. Generally, the arrays consist of individual LED elements arranged in an X-Y grid on a substrate.
While solid state lighting sources generally operate at cooler temperatures than the traditional arc lamps, some issues with thermal management exist. The useful lifetime of LEDs are significantly affected by their junction temperature. In certain situations the cooling system of the LEDs may fail catastrophically and unless power applied to the LEDs is immediately removed, the junction temperature may reach a level that causes significant and permanent degradation to the module or may even cause the light module to fail. Typically, a thermal switch of some kind may be mounted on the package of a solid state lighting module. When the operating temperature of the module reaches a certain level, the thermal switch interrupts the flow of power to the module to avoid damaging the module. The problem with a thermal switch is that it must be placed very near the LED to quickly recognize a cooling system failure. This forces the light module designer to sacrifice good design for the sake of safety and in some cases renders the light module ineffective. More generally there is a compromise which relegates the physical position of the thermal switch to a location generally removed from the LEDs which causes a significant lag in the time at which the LEDs experience a very high temperature and the time which the thermal switch can respond to that temperature increase, potentially causing significant degradation to the light module. This problem is drastically more important in the field of solid state UV curing where LEDs are operated at relatively high power levels and thus reducing the time between losing cooling and light module failure, making the thermal switches even more important.